diff --git a/1623/41/survey.htm b/1623/41/survey.htm
index 6d81aae4a..a0937d505 100644
--- a/1623/41/survey.htm
+++ b/1623/41/survey.htm
@@ -45,10 +45,10 @@ provide independent checks. The only known problem with the published
 survey is the section of passage drawn 46° out due to the "fridge
 north" calibration cock-up.</p>
 
-<p>After the high entrances of <a href="/1623/143/143.htm">143</a> and
+<p>After the high entrances of <a href="/1623/143/143.html">143</a> and
   <a href="/1623/41/144.htm">144</a> were explored, and the latter was connected
 into Stellerweg, and considerably more exploration was done in
-<a href="/1623/142/142.htm">142</a>, including two connections into the main
+<a href="/1623/142/142.html">142</a>, including two connections into the main
 system, a lot more survey data was available, all of it above the Big Rift in
 Stellerweg. All these passages were drawn up, at a larger scale than the
 original published survey, and with the fridge north error corrected.